System and method for satellite based controlled ALOHA

ABSTRACT

A system and method for satellite based controlled ALOHA is provided. The system and method configure VSATs so that they accept guidance from a centralized and/or distributed system controller to determine when, where, and/or on what portion of a satellite resource to attempt to access a channel. The system and method take advantage of traffic patterns to maximize efficiency by utilizing a centralized and/or distributed control to determine which VSATs are and are not currently active, and to allocate to a portion of the inbound channel to the active VSATs and a portion of the inbound channel to the inactive VSATs. In a distributed approach, each VSAT decides for itself whether it captures a certain part of the inbound resource or not. This decision can be made based on previous transmissions that went through the part of the inbound intended to be captured.

The present application claims priority from provisional application60/211,475 filed Jun. 15, 2000 and provisional application 60/225,307filed Aug. 15, 2000, the contents of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the field of satellite multi-accesscontrol mechanisms and, more particularly, to apparatuses and techniquesfor controlling random access to satellite communication networks.

2. Description of Related Art

Various types of multiple access schemes are known to allow multipleusers to utilize satellite communication system resources.

A substantial improvement to the basic ALOHA system is described in U.S.Pat. No. 5,053,782('782 patent) having a common assignee as the presentapplication. Other variants of the ALOHA scheme include U.S. Pat. No.5,084,900 ('900 Patent) and U.S. Pat. No. 5,138,631 ('631 patent) toSpacenet, a subsidiary of the present assignee.

Coordinating the data transfer from the hub to the VSATs (outbound) isrelatively simple because the hub is a unique source of information.However, coordinating the data transfer from the VSATs to the hub(inbound) is significantly more complex particularly where there arethousands, tens of thousands, or even hundreds of thousands of terminalsvying to access the same satellite resources in a non-synchronizedmanner. There is a need for a satellite network to connect a very largenumbers of very small aperture terminals (VSATs) and one or more centralstations (hubs) via a two directional communication satellite link.Current schemes are limited in their performance. In particular, themaximal utilization under a given response time constraint is limited.Thus, there is a need for a system and method for a multiple accessscheme which allows a very large number of remote stations withinfrequent bursts of data to communicate over a shared VSAT channel in amore efficient way than currently known multiple access schemes provide.Further, the system needs to be inexpensive so that it may deployed in amass market bringing the benefits of VSAT technology to the averageconsumer.

SUMMARY OF THE INVENTION

Aspects of the present invention solve one or more of the above-statedproblems and/or provide improved systems and methods for implementing asatellite network architecture.

Aspects of the present invention include configuring VSATs to acceptguidance from a centralized and/or distributed system controller todetermine when, where, and/or on what portion of a satellite resource toattempt to “capture” a channel. This may be a specific instruction, butpreferably includes a range of appropriate time, frequency, and/or otherresources which the remote VSATs may be configured to randomly chooseresponsive to guidance from a control system. Aspects of the presentinvention have been termed “controlled ALOHA” to indicate that the ALOHAscheme is controlled to gain the efficiency advantages of the dedicatedchannels for more active connections along with the efficiencyadvantages of a pure ALOHA system for the truly random accesses by alarge body of substantially non-active terminals.

In further aspects of the present invention, a recommendation may bemade to a subset of the total VSAT terminals, typically a subset ofactive VSAT terminals, to try to capture (e.g., when and/or where) aparticular portion of a medium resource in which to transmit. In thismanner, a single channel may have dual channel characteristics in thatit may both act as a “dedicated” and random access manner at the sametime. Certain properties of real traffic patterns cause the presentinvention to provide improved performance, such as throughput/delaycharacteristics, over known variations of the ALOHA technique. Thepresent system is particularly advantageous in satellite systems wherethere are long delays between the VSAT terminals and a central locationsuch as one or more Hubs, delays that prohibit carrier sense techniquesto improve ALOHA. Thus, controlled random access (CRA) provides anetwork dedicated access like functionality, but without allocating aresource to a VSAT in a dedicated, collision free manner.

Aspects of the present invention are particularly useful in, forexample, direct-to-home VSAT systems (or other similarly situatedsystems) where traffic pattern are such that only a small fraction ofthe VSATs are actually using the inbound link at any given time interval(e.g., a time-interval of one or two minutes). For example, in adirect-to-home system, only a small fraction of the overall customers(e.g., internet users) may be transmitting data at any one given timeinterval. Thus, during any given time-interval, most of the inboundtraffic is generated by a very small percentage of the overall number ofVSATs in the system. The set of active VSATs slowly varies over time(some of the active VSATs become inactive while other inactive VSATsbecome active). In any event, given a large enough population of VSATs,the number of active VSATs, remains relatively small but varies overtime.

The present invention takes advantage of this traffic pattern tomaximize efficiency by utilizing a centralized (e.g. in the hub) and/ordistributed control to determine which VSATs are and are not currentlyactive, and to allocate to a portion of the inbound channel to theactive VSATs and a portion of the inbound channel to the inactive VSATs.This allocation may be variously configured.

In one aspect of the invention, the currently active VSATs may notrandomize their transmissions over the entire inbound capacity. Rather,each of the active VSATs may be assigned a portion of the inboundcapacity. Thus, the active VSAT may transmit on a predetermined portionof the inbound capacity (rather than randomly) whenever the VSAT hasinbound data to transmit (such as a data frame of information). In thismanner, each of the active VSATS may be assigned a predetermined inboundresource and may not collide with other active VSATS. Aspects of theinvention include allocating some and/or all of the inbound channelcapacity to active VSATs. In these aspects of the invention, theinactive VSATs may be configured to randomize their transmissions, ifthey have any, over the whole inbound capacity. In these aspects of theinvention, the active VSATs may not collide between themselves, butcollisions may occur between transmissions of active VSATs and currentlyinactive VSATs, and between transmissions of inactive VSATs andthemselves.

Aspects of the invention discussed above allow the satellite channel tobe much more efficient in that the number of collisions is substantiallyreduced over other satellite communication schemes. The only collisionsthat are permitted to occur involve inactive VSATS rather than thecurrently active VSATS. Thus, the overall efficiency of the satellitecommunication channel is substantially improved, particularly forsatellite network configurations with long delays and many terminals.

Thus, the present invention provides the use of the same channelsimultaneously in a random access mode (e.g., ALOHA) and in a dedicatedmode (e.g., reservation allocation). Thus, in networks according to thepresent invention, while one VSAT is using the Inbound resource in areserved-like mode, some (e.g., non-active) and/or all other VSATs areallowed to use the Inbound resource at the same time in a random manner.In this fashion, the system and method of the present inventioncontrasts sharply with known reservation-like schemes where a singleVSAT is allowed to use the allocated resource, and all other VSATs areinformed (explicitly or implicitly) of that, and therefore don'tinterfere with the single VSAT transmissions.

Controlled random access reduces the average collision probability inthe Inbound. For a given Inbound capacity, the delay characteristics mayalso be substantially improved. Aspects of the present invention reduceinbound capacity requirements for a given delay (i.e., a given collisionprobability). In other words, the present invention improves thethroughput-delay characteristics of the conventional ALOHA channel,particularly for use with a large number of VSAT terminals having burstdata characteristics of a medium to long characteristic. Controlledrandom access may be used with one and/or two dimensional ALOHA systems.

In further aspects of the invention, controlled random access avoidsexplicit requests of reserved capacity by the VSATs. This reducestraffic as well as eliminates the need to pause the VSAT data transferfrom the time the VSAT requests for reservation until the time the VSATreceives the resource allocation. The VSAT does not have to estimate orpredict the amount of data the VSAT expects to carry or to obtainreserved resources for, as is the case for reservation requestsassociated with a specified data amount (“transaction reservation”).Likewise, aspects of the invention do not require the VSAT to send amessage to release the resource, as is the case for reservations andallocations that do not indicate data amount to be transferred (“streamreservation” or “circuit switch”). Thus, overall performance issubstantially improved.

Thus, there is described aspects of the invention in whichimplementation variants simultaneously utilize allocated capacity andrandom access capacity of an Inbound channel.

The Controlled ALOHA scheme of the present invention can be implementedin several ways, central, distributive, or a combination of these two.According to a centralized approach, a central algorithm is as describedbelow. In this approach, aspects of the invention utilize a centralentity, such as the hub, to gather VSATs traffic statistics, identifyactive VSATs, and allocate inbound resources among the VSATs.

In alternative aspects of the invention, a distributed approach isutilized. According to a distributed approach, there may be little or noinvolvement of a central entity. Instead, each VSAT decides for itselfwhether it captures a certain part of the inbound resource or not. Thisdecision can be made based on previous transmissions that went throughthe part of the inbound intended to be captured. If a previoustransmission (or previous transmissions) in this part of the inboundresource was successful (i.e., a collision did not occur), the VSAT maydecide to control this inbound part, and its sequel transmissions may beusing this particular part of the inbound resource. If transmissions inthis part collide, the VSAT decides not to control it. The distributedapproach is advantageous in that performance of the control mechanismsis enhanced since there is no need for a centralized location tocoordinate each of the VSATs. Rather, each VSATs capture parts of theshared capacity in a distributive manner independently of every otherVSAT.

In still further aspects of the invention, each VSAT decides for itselfwhether it should get a controlled random access channel, request it,and the hub allocates the channel to the requesting VSAT. The VSAT maymake the decision based on statistical analysis or the level of itscache.

Thus, these and other aspects of the invention may become apparent byreference to the Figures and Detailed Description of the preferredembodiments described below. Numerous inventions and alternative aspectsof the inventions are described throughout the specification. Theseinventions may be claimed at any time in the future and the ability tomodify the combinations and sub combinations claimed are not intended tobe limited by the currently appended claims. The described inventionincludes one or more elements from the apparatus and methods describedherein in any combination or sub combination. Accordingly, there are anynumber of alternative combinations for defining the invention, whichincorporate one or more elements from the specification in anycombinations or sub combinations. Other ways to implement one or moreaspects of the present invention may be apparent to those skilled in theart and include combinations of the approaches described above.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a typical satellite communication environment showing alarge number of diverse two-way residential VSAT systems vying for thesame satellite resources in accordance with the present invention.

FIG. 2 shows an analysis of the CRA theoretical performanceimprovements.

DETAILED DESCRIPTION

Referring to FIG. 1, a satellite communication system 1 is shown havinga hub site 2 and a plurality of remote sites 3-3N. In preferredembodiments, the remote sites 3 reside at a residence 15 and include asmall VSAT antenna 14, a satellite transceiver 4 and a plurality ofperiphery devices such as computer 5, television 6, and telephone 7. Theresidence preferably includes a home, but may be variously configured toinclude a business, office, or other location. In some embodiments, thetransceiver 4 may be configured as an adapter card in a personalcomputer such as is shown in remote site 3N. In exemplary systems,hundreds of thousands or even millions of residences 15 may beinterconnected using one or more satellite networks 3. The receiver mayprovide decoding for internet and/or other two-way data for a personalcomputer, one or two-way cable television signals, and telephony data.The telephony data may be IP telephony or a simulated conventional plainold telephony (POTS) interface.

The communication paths to the satellite may be one or more low speeduplink channels (inbound) 20 and one or more high speed down-linkchannels (outbound) 21. The inbound and outbound channels preferablyoriginate from one or more hub sites 2. The hub site 2 may include oneor more antennas 23, hub circuitry 24 such as one or more satellitemodems, processing computers, storage, cache servers, and/or otherprocessing resources. The hub circuitry may interface to a plurality ofexternal networks 26 such as the public switched telephony network(PSTN), Internet, frame relay networks, ATM networks, and/or X.25networks. For example, the gateways 25 may include a cable TV gatewayproviding, for example, a frame relay connection for coupling cabletelevision signals from a remote content site to and/or from the HUBsite using a frame relay network. The gateways 25 may also include aPSTN gateway for coupling the one or more telephones 7 in one or moreremote sites 3 to the public switched telephone network (PSTN) byproviding appropriate connections to one or more SS7 signaling systemsand associated switched connections. Similarly, the computers 5 at theremote sites may be coupled to the Internet and/or directly to a remotebusiness network using, for example, IP tunneling and/or a direct ATMconnection by providing an Internet and/or ATM gateway at the hub site2.

In this manner, the remote site 3 has complete connectivity whilebypassing the telephone company and local cable operator. Thus, a remotesite has total freedom to operate unconnected from the local suppliersand associated price structures and system constraints. In this manner,the satellite network 3 may provide the end user with 500 or moreinteractive television channels, high speed internet service, unlimitednumber of telephone numbers and other services at a lower cost thanconventional suppliers.

In order to enable the satellite network to operate cost effectively, anew access system and method is needed. In exemplary embodiments, thereceiver 4 may begin in an inactive inbound state. In this state, it mayhave no need to access the inbound channel 20 but may receive data, suchas television programming, from the outbound channel 21. When the userdesires to access the inbound channel 20 such as by requesting Internetdata, making a phone call, and/or accessing a two-way televisionfeature, the receiver 4 tries to capture an inbound resource from theinbound channel 20. This may be done by contending for one or more ofthe inbound resources and transmitting inbound data to the hub site. Ifa collision occurs, the transmission may occur again at random/pseudorandom times and/or using random/pseudo random inbound resources untilsuch time as the remote site 3 is successful in capturing an inboundresource.

Where the transceiver monitors its internal cache and/or other criteriato help determine that there is a high likelihood that the site isinitiating a moderate to long transmission (e.g., where the remote sitehas initiated a telephone call, web access, and/or a file transfer), theremote site may itself request allocation of a assigned inboundresource. Alternatively, once the remote site has been active for apredetermined period of time and/or sufficiently active during any onesliding window, the hub site may respond and/or directly allocate aninbound resource to the remote site. Once the inbound resource has beenallocated to one remote site 3, the currently active remote site may nolonger randomize its inbound transmissions over the entire inboundcapacity. Rather, the active remote site 3 may now assigned a portion ofthe inbound capacity and thus transmits on a predetermined portion ofthe inbound capacity (rather than randomly) whenever the remote site hasinbound data to transmit. In a similar fashion, each other remote sitewhich becomes active is assigned a similar, but different, portion ofthe inbound resources. In this manner, each of the active remote sitesmay not collide with other active remote sites. When a site is no longeractive, e.g., when the file transfer has completed, the site and/or hubreleases the resource previously assigned to the active site forreallocation.

The inactive remote sites may be configured to randomize theirtransmissions, if they have any, over the whole inbound capacity(including the inbound capacity assigned to active sites). Thus, theactive remote sites 3 are configured so that they do not collide witheach other, but may collide on occasion with inactive remote sites 3.Additionally, inactive remote sites may themselves collide with eachother.

Embodiments of the present invention typically are not implemented on ademand assignment basis where a channel is demanded and assigned to aparticular remote site 3 on a semi-permanent basis. Demand accesssystems are very cumbersome and not well suited to data which has shortlength and burst characteristics. However, in certain situations, it maybe desirable to utilize the controlled random access mode (activesites), random access mode (for inactive sites), and demand assignment(fixed channel capacity) for certain constant on sites which may beprovided out-of-band such that each mode may coexist on a single system.

Packets transmitted on a channel in accordance with embodiments of thesatellite network 1 described herein may not be free of collisions. Insome embodiments, other remote sites (for which a channel has not beenallocated) can still transmit on the same inbound resource such asfrequency and/or timeslot. The active remote sites 3 may still collidewith the inactive remote sites 3 and the inactive remote sites 3 maystill collide with each other. The controlled random access schemeimplemented by the present satellite network 1 may be most appropriatefor networks where, at any given time, most of the traffic is created bya small number of active remote sites, but may still have burst trafficof short duration from a very large number of remote sites.

The satellite network 1 can be implemented in a centralized manner withthe hub site 2 determining both the threshold criteria for determiningan active site and the allocation of resources. In this approach,embodiments of the invention utilize a central entity, such as the hubsite 2, to gather traffic statistics from the various remote sites 3,identify active remote sites 3 from the traffic statistics, and allocateinbound resources among the active remote sites 3 and then inform everyother remote site 3 of the allocation.

Alternatively, the satellite network 1 may be implemented in adistributive manner with the remote site determining when it has passeda threshold of becoming an active site, vie for and capture an inboundresource, and inform every other remote site that the inbound resourcehas been captured. This embodiment of the invention may be utilizedwhere every remote site receives the same satellite signals bounced offof the satellite as the hub site 2, or where the hub or switchingsatellite informs the allocation. Thus, in some embodiments the remotesites 3 may act in a completely distributed manner without input fromthe hub site 2. In embodiments utilizing this approach, there may belittle or no involvement of a central entity. Instead, each VSAT decidesfor itself whether it captures a certain part of the inbound resource ornot. This decision can be made based on previous transmissions that wentthrough the part of the inbound resource intended to be captured. If aprevious transmission (or previous transmissions) in this part of theinbound resource was successful (i.e., a collision did not occur), theremote site may decide to control this inbound part, and its sequeltransmissions may be using this particular part of the inbound resource.If transmissions in this part collide, the remote site decides not tocontrol it. The distributed approach is advantageous in that performanceof the control mechanisms is enhanced since there is no need for acentralized location to coordinate each of the remote sites.

In still further embodiments of the invention, each remote site monitorsthe nature and type of transmission and notifies the hub site that ithas become active and is likely to have a medium to long transmission.The hub site 2 may then take over and allocate a portion of the inboundresources to the newly active remote site 3. Thus, the control for thesatellite network 1 may be divided between the remote sites and the hubsites with each doing that portion of the control task which it isoptimized to control. Hence, each remote site decides for itself whetherit should capture a controlled random access channel (become active),request the channel, and the hub allocates the channel to the requestingremote site. In this manner, if the remote site has only a very smallamount of data, such as an acknowledgement or a couple of bytes totransmit, it knows immediately that it does not need semi-exclusive useof a resource and hence does not request one from the hub site 2.

One preferred embodiment of the satellite network 1 in accordance withthe present invention is discussed below in some detail. This embodimentis exemplary in that other embodiments and variations in accordance withthe present teachings may be apparent to those skilled in the art.

The controlled random access satellite network 1 may be configured toprevent much of the inbound packets' collisions by allocating a fixedresource such as frequency and/or time slot for the remote sites 3 inthe network which generates the most inbound traffic. In this manner, itis possible to prevent packets generated by the most active remote sites3 from colliding with each other, thus preventing most of the collisionin the network. Statistically, it is often the case that more then 80%of the network traffic at any given time is generated by a small numberof remote sites. The number of the remotes sites is actually so smallthat one can allocate a fixed frequency, time slot, and/or otherresource for every such active remote site, thus eliminating all thecollisions between packets from these remote sites. Where 80% of thenetwork load is among the active sites, many if not most collisions maybe avoided, and the network throughput is likely to increasedramatically.

Where there is an unusual burst of traffic (e.g., mothers day or a majordisaster where the phone is utilized extensively), there may besituations where there are more active remote sites 3 than resources. Ifthe there are more active remote sites than inbound resources, eachremote site may be allocated only a “mini-slot” (e.g., a portion of theinbound resource). For example, each remote site 3 may be allocated atime slot every third frame and/or a frequency intermittently. Thus,each active remote site 3 may be allocated only part of an inboundresource.

Where channel overload is approaching, the system may allocate inboundslots to voice traffic first, followed by data traffic. In this manner,voice calls may not be lost and data transmissions may simply bedelayed.

Example Definitions

In this example, the following terms maybe utilized:

-   -   CRA channel—a frequency, used for random access (CRA)        transmission, on which remote sites 3 may transmit packets when        using the controlled random access scheme    -   Multi-slot—a number of time-slots, as used by the partial demand        assignment mechanism.    -   Mini-slot—one time-slot in a multi-slot cycle, i.e. one        time-slot every multi-slot time-slots.    -   CRA slot—a mini-slot in a controlled random access channel. This        may be the basic allocation unit and may be a time slot within a        certain uplink frequency.    -   CRA allocation—The process of allocating controlled random        access channels to a remote site.    -   active remote site—a remote site to which at least one        controlled random access slot was allocated.    -   Inactive remote site—a remote site in which no CRA slot was        allocated.    -   CRA allocation table—a mapping between available CRA slots in        the system and the remote sites to which they have been        allocated.    -   Load (of a remote site)—a numeric value, which may indicate the        amount of inbound traffic the remote site generates.        Exemplary CRA Implementation

In order to implement the CRA access scheme in the hub site 2 (and/orthe remote sites in a distributed scheme), it may be desirable toperform one or more of the following activities:

-   -   Load calculation—the hub site 2 may calculate the load of every        remote site and may retain this value in memory in any suitable        table such as a data structure. In exemplary embodiments, the        data structure may be defined as the data structure. The load of        every remote site may also be correlated with the last time slot        in which a burst was last received from this remote site.    -   Announcing CRA allocation changes to remote sites—the hub site 2        may announce the changes in the CRA allocation table in the AA        message of the last mini-slot in the multi-slot (when the load        calculation may be carried out).    -   Keeping remote sites consistent with the hub site 2 CRA        allocation tables may be updated in every inbound frame (sent by        the remote site) and may include the remote site link state such        as random access, assigned inbound resource, CRA frequency and        other parameters) to inform the hub site 2 of the remote site        state as the remote site knows it. The hub site 2 may notify        every remote site in every frame whether it is in CRA mode by        including a 1-bit CRA on/off indicator for one or more remote        sites.        CRA Channels

In exemplary embodiments, the hub site 2 may need to know the number andfrequencies of all CRA channels the remote sites can transmit on. Forexample, a first group of remote sites may be able to transmit on afirst group of frequencies, a second group of remote sites on a secondgroup of frequencies, a third group of remote sites on a third group offrequencies, and so forth. Where the hub site requires this information,it may be stored in one or more configuration files and/or in the datastructure. The channels may be defined in accordance with the receiverscapabilities and their number can vary in accordance with the number ofcurrently active channels and the capabilities of the remote site. Thenumber of channels a group of remote sites requires depends heavily onthe system unique traffic characteristics.

In exemplary embodiments, the hub allocates and otherwise manages a poolof controlled random access frequencies/sub channels. The CRA channelsconfiguration may include such items as the type and/or quantity of CRAchannels, the number of CRA channels which maybe allocated to aparticular site, the inbound and/or outbound frequencies a remote siteis configured to receive. For each active site, the allocation of aninbound resource may include the same allocation process. For example, aCRA slot (on a certain CRA channel) may be allocated to a remote site ifand only if the remote site belongs to the same inbound band. Thecentral site may or may not check to determine whether the receiver canreceive certain allocated frequencies. In some embodiments, it may bedesirable to have the receiver receive the correct frequencies for anyparticular remote site. The remote site may have one and/or a pluralityof bit rates. Where the remote site is capable of multiple bit rates,the hub site 2 may allocate a plurality of inbound resources to theremote site, depending on overall system load.

For some sites, it may be desirable to define certain predefinedparameters. For example, certain sites may only have two way cabletelevision and thus have carefully defined traffic parameters. In thesesites, short bursty traffic will be most common if not the exclusivetransmission mechanism. Thus, the satellite network 1 may be configuredsuch that these sites may never become active sites. Other sites mayonly have telephone connections, and thus every active site is likely tobe an active site once a connection is initiated. Further, it ispossible to tailor the inbound resources to the requirements of aparticular site. For example, a small business may pay additional moneyto have a committed information rate for its inbound link. In thissituation, the designated remote site maybe allocated X number ofmini-slots and/or channels each time that it becomes active.

Certain other parameters may also be defined such as a hysteresiswhereby a site may remain an active site for X number of time slotsand/or other measures such as windows and/or time after it is no-longeractive (e.g., falls below the definition of an active site). In thismanner, where the user stops to look at a web page or pauses speaking ina phone call, the active site status of the remote site is not lost.This hysteresis may be variable depending on the type of traffic. Forexample, the hysteresis may be defined as falling within 8 or fewerframes. The hysteresis parameter may be used to avoid rapid mode changesof remote sites. In still further exemplary embodiments, a remote sitemay be allocated a CRA channel if and only if its load value is largerthan the minimum load value of all active remote sites plus a hysteresisvalue.

Additional set-up parameters may also be provided such as a loadingfactor for certain remote sites. For example, the remote site actualtraffic may be multiplied by a loading factor (e.g. 2, 4, or 8) suchthat the site becomes active more quickly than other remote sites. Inthis manner, certain remote sites may be provided with favorabletreatment with respect to other remote sites. Other parameters which maybe varied include the refresh interval after which the load of all theactive remote sites may be re-calculated even if no packets werereceived from them. This defines the interval over which to determinewhether to remove remote sites that are no longer active from the CRAallocation table. The number of mini slots within a multi-slot channelmay also be controlled such that the number to allocate to a particularremote site maybe selected.

Synchronizing Multi-Slot Counters

In exemplary embodiments, certain remote sites may include a mechanismto receive mini-slot allocations. In one embodiment, a multi-slotcounter may be utilized. The multi-slot counter may be implemented bysynchronizing the counter with other remote sites and/or with the hubsite 2. This maybe done through various mechanisms such as utilizing thelink connect message generated by the remote sites and including aremote site multi-slot counter in the message. The hub site 2 maygenerate a response, including the remote site's multi-slot countercorrection in the next frame. These two frames maybe consecutive, i.e.whenever a message is fragmented they may have to both be included inthe one fragment.

If a remote site receives a query (e.g., an “open up” message), it mayrespond with a message (e.g., “connect” message) providing an indicationof the contents of its multi-slot counter. However, as opposed to theabove situation, the remote site might not receive the frame with theresponse. In such a case, the multi-slot counter of the remote site maynot be synchronized with the hub site 2. Therefore, a remote site maycheck before every transmission that its multi-slot counter issynchronized, and if not it may synchronize it before sending any data.

Calculating Load

The load of the remote site may be calculated using any known techniqueconsistent with the controlled random access system. In theory, it maybe desirable to compute the load of the remote sites according to thefollowing formula:

L_(new) = L_(old)(1 − τ)^(n) + τWhere TAU represents a configurable constant, n is the number oftime-slots since the last time-slot on which a packet was received fromthis remote site and L-old is the previous load value of the remotesite. In alternate calculations, the above load calculations may beperformed using a normalizing constant M having a value such as 65,000and using a time constant N, which is the number of time-slots in Tseconds (where T is a configuration parameter). In these calculations,it may be desirable to define TAU as 1/N. Thus, the load calculationsmay be performed using the following formula:

L_(new) = L_(old) * M * (1 − 1/N)^(n) + M/N

Performance is always a concern when performing load calculations for alarge number of remote sites. This is particularly useful in the presentinvention where load determinations are often required to be made veryquickly. Accordingly, in embodiments of the present invention, the loadcomputations may be made using a look-up table. The look-up table maystore the values of M*(1−1/N)^n for all valid n values (up to N), forexample. In this manner, the load calculations are substantiallyimproved.

New Data Structures

To implement the CRA channel allocation at the hub site 2 it isdesirable to formulate new data structures. For example, it maybedesirable to include the number of frequencies that the receiver iscapable of utilizing and the number of mini-slots the receiver mayreceive. Additionally, the data structure may include the total numberand identification of free inbound resources such as channels andmini-slots. The data structure may also include the minimum and assignedmaximum load value allocated to each remote site, the current inboundresources allocated to a particular remote site (e.g., one or morechannels and/or mini-slots), whether the remote site may become anactive site, and whether the remote site has any weighting factorsassociated with its load calculations.

The data structure may include in the same and/or a separate datastructure a list of all remote sites from which a packet was receivedduring the last measure increment such as a multi-slot time period,window, or other periodic measure. The data structure may also includetheir current load value after the most recent packet and/or other unitof data was received. If the current load value is larger than theminimal load of all the remote sites in the currently active allocationtable, the site maybe moved to a active sites table. Conversely, if theload value is not sufficient, the remote site may remain in an inactivesite table.

In exemplary embodiments, the inactive remote sites table may supportthe following operations: initialization, insert new remote site intodata structure, returns minimal and/or maximum load for all remote sitesin the inactive remote site data structure, removes and/or adds aspecified remote site to the inactive remote site data structure.

To keep the required statistics and telemetry values, the datastructures may also include: statistics and telemetry values, number orretry values for each inbound link, number of received bursts per timeslot, the number of time-slots and/or burst data associated with thehistogram, the last timeslot a packet was received from the remote site,the load of the remote site, the configuration of the remote site(television, data, telephony), the number of times an active remote sitedesignation was allocated to this remote site (either absolute or perrecent time period), the time of day associated with active status for aparticular remote site, the minimal number of time slots during which aninbound resource was allocated to this remote site, the maximal numberof time slots during which an inbound resource was allocated to thisremote site, the total number of time slots during which a CRA channelwas allocated to this remote site (used for the average calculation).

Exemplary Implementation Methods

The satellite systems 1 may include one or more methods ofimplementation. For example, the satellite system may include aninitialization sequence, a response to packet arrival, a response to endof a multi-slot period, and a sequence to deal with a remote site goinginactive, and a sequence which occurs periodically such as after every“refresh interval”.

Initialization: Upon initialization, the CRA allocation table maybeinitialized, the inactive remote site table may be initialized, and theL look-up table may be calculated.

Upon packet arrival: When the hub site 2 receives an inbound packet froma remote site, it may first calculate its new load value and update itsvalue in the remote site's data structure. Then it may check to see ifthis remote site is a “active” remote site (i.e. if it already receiveda inbound resource allocation). If so, it may update its load value atthe CRA allocation table. If not, it may check if its new load value ishigher then the minimal load of all remote sites in the active siteallocation table. If so, it may add it to the active remote sites table(if it wasn't in it already), or update its load in it (if it alreadywas in it).

End of multi-slot: The hub site 2 may insert remote sites from theinactive remote sites table into the active site allocation table, aslong as their load value is larger then the minimal load of all theremote sites in the active site allocation table. All the remote sitesthat were inserted/removed to/from the active site allocation table maybe notified in the next message of their status change.

When a remote site goes active/inactive: When hub site 2 receives alink-connect message from a remote site, it may synchronize multi-slotcounters as discussed above. Then it may nullify the remote site loadvalue at its data structure. When a remote site goes off-line, it may beremoved from the active site allocation table and/or the inactive remotesites table.

Every “refresh interval”, the hub site 2 may re-calculate the load forall the remote sites in the active site allocation table, in order todecrease the load values of remote sites that haven't transmitted for along time. This calculation may have to be synchronized with the aboveoperations.

FIG. 2 shows an analysis of the CRA theoretical performanceimprovements. The mathematical model is described in FIG. 2 approximatesthe performance of the CRA system. The table at the bottom of FIG. 2shows that for a given collision probability of 30% (this is 70% successprobability) the well know ALOHA (or RA) provides 25% throughput whilecontrolled RA is almost twice as efficient −48.7% throughput, hencerequires in theory half the space segment (bandwidth) that's needed forRA.

Having described several embodiments of the system and method forsatellite based controlled ALOHA in accordance with the presentinvention, it is believed that other modifications, variations andchanges will be suggested to those skilled in the art in view of thedescription set forth above. It is therefore to be understood that allsuch variations, modifications and changes are believed to fall withinthe scope of the invention as defined in the appended claims.

1. A system for communicating with a large number of remote satellitelocations comprising: a plurality of a first set of remote terminaldevices; a plurality of second remote terminal devices operating in adedicated mode using the same overlapping channels; and a hub site whichdetermines threshold criteria for determining when said remote terminaldevices are active, and allocates said channels, wherein when said oneof said plurality of second remote terminal devices has beensufficiently active during a sliding window, said one of said pluralityof second remote terminal devices directly accesses said channels,wherein collisions between inbound packets from different ones of saidfirst and second remote terminal devices are prevented by allocating oneof frequency, time slot, and frequency and time slot to said ones ofsaid first and second remote terminal devices that generate the mostinbound traffic, wherein when there are more active ones of said firstand second remote terminal devices than there are channels, each of saidfirst and second remote terminal devices is allocated a mini-slot,wherein said hub site calculates load for each of said first and secondremote terminal devices and retains loads in memory, and wherein saidhub site correlates loads for each of said first and second remoteterminal devices with the last time slot in which a burst was lastreceived from each of said first and second remote terminal devices, andmaintains said correlated loads in an allocation table.
 2. A system forcommunicating with a large number of remote satellite locations asrecited in claim 1, wherein said hub site transmits changes to saidallocation table to said first and second remote terminal devices.
 3. Asystem for communicating with a large number of remote satellitelocations as recited in claim 1, wherein said hub site updates saidallocation table every inbound frame.
 4. A system for communicating witha large number of remote satellite locations comprising: a plurality ofa first set of remote terminal devices; a plurality of second remoteterminal devices operating in a dedicated mode using the sameoverlapping channels; and a hub site which determines threshold criteriafor determining when said remote terminal devices are active, andallocates said channels, wherein when said one of said plurality ofsecond remote terminal devices has been sufficiently active during asliding window, said one of said plurality of second remote terminaldevices directly accesses said channels, wherein collisions betweeninbound packets from different ones of said first and second remoteterminal devices are prevented by allocating one of frequency, timeslot, and frequency and time slot to said ones of said first and secondremote terminal devices that generate the most inbound traffic, whereinwhen there are more active ones of said first and second remote terminaldevices than there are channels, each of said first and second remoteterminal devices is allocated a mini-slot, and wherein said first andsecond remote terminal devices comprise a multi-slot counter, saidmulti-slot counter in each of said first and second remote terminaldevices being synchronized with said hub site and each of said first andsecond remote terminal devices.
 5. A system for communicating with alarge number of remote satellite locations comprising: a plurality of afirst set of remote terminal devices; a plurality of second remoteterminal devices operating in a dedicated mode using the sameoverlapping channels; and a hub site which determines threshold criteriafor determining when said remote terminal devices are active, andallocates said channels, wherein when said one of said plurality ofsecond remote terminal devices has been sufficiently active during asliding window, said one of said plurality of second remote terminaldevices directly accesses said channels, wherein collisions betweeninbound packets from different ones of said first and second remoteterminal devices are prevented by allocating one of frequency, timeslot, and frequency and time slot to said ones of said first and secondremote terminal devices that generate the most inbound traffic, whereinwhen there are more active ones of said first and second remote terminaldevices than there are channels, each of said first and second remoteterminal devices is allocated a mini-slot, wherein said hub sitecalculates load for each of said first and second remote terminaldevices and retains loads in memory, and wherein said load (L_(new)) foreach of said first and second remote terminal devices is calculatedaccording to the following formula: L_(new) = L_(old)(1 − τ)^(n) + τ,where τ is a configurable constant, n is the number of time slots sincethe last time slot on which a packet was received from a remote terminaldevice, and L_(old) is the previous load value of the remote terminaldevice.
 6. A system for communicating with a large number of remotesatellite locations comprising: a plurality of a first set of remoteterminal devices; a plurality of second remote terminal devicesoperating in a dedicated mode using the same overlapping channels; and ahub site which determines threshold criteria for determining when saidremote terminal devices are active, and allocates said channels, whereinwhen said one of said plurality of second remote terminal devices hasbeen sufficiently active during a sliding window, said one of saidplurality of second remote terminal devices directly accesses saidchannels, wherein collisions between inbound packets from different onesof said first and second remote terminal devices are prevented byallocating one of frequency, time slot, and frequency and time slot tosaid ones of said first and second remote terminal devices that generatethe most inbound traffic, wherein when there are more active ones ofsaid first and second remote terminal devices than there are channels,each of said first and second remote terminal devices is allocated amini-slot, wherein said hub site calculates load for each of said firstand second remote terminal devices and retains loads in memory, andwherein said load (L_(new)) each of said first and second remoteterminal devices is calculated according to the following formula:L_(new) = L_(old) * M * (1 − 1/N)^(n) + M/N where M is a normalizingconstant M, N is a time constant, which is the number of time slots in Tseconds (where T is a configuration parameter), τ is 1/N, n is thenumber of time slots since the last time slot on which a packet wasreceived from a remote terminal device, and L_(old) is the previous loadvalue of the remote terminal device.
 7. A system for communicating witha large number of remote satellite locations as recited in claim 1,wherein said allocation table comprises information relating to a numberof frequencies a remote terminal device is capable of utilizing, anumber of mini-slots said remote terminal device may receive, a totalnumber and identification of free inbound ones of said channels andmini-slots, a minimum and assigned maximum load value allocated to eachof said first and second remote terminal device, current inboundresources allocated to each of said plurality of first and second remoteterminal devices, whether said remote terminal device may become anactive site, and whether said remote terminal device has any weightingfactors associated with its load calculations.
 8. A system forcommunicating with a large number of remote satellite locations asrecited in claim 1, wherein said allocation table comprises a list ofall remote sites from which a packet was received during a last measureincrement.
 9. A system for communicating with a large number of remotesatellite locations as recited in claim 8, wherein said measureincrement is one of a multi-slot time period and window.
 10. A methodfor communicating with a large number of remote satellite locations,comprising the steps of: simultaneously communicating in random accessmode with a plurality of a first set of remote terminal devices andcommunicating with a plurality of second remote terminal devices in adedicated mode using the same overlapping channels; determiningthreshold criteria at a hub site to determine when said first and secondset of remote terminal devices are active; and allocating said channels;calculating load at said hub site for each of said first and secondremote terminal devices and retaining loads in memory; and correlatingsaid loads at said hub site for each of said first and second remoteterminal devices with the last time slot in which a burst was lastreceived from each of said first and second remote terminal devices; andmaintaining said correlated loads in an allocation table.
 11. A methodfor communicating with a large number of remote satellite locations asrecited in claim 10, wherein said hub site transmits changes to saidallocation table to said first and second remote terminal devices.
 12. Amethod for communicating with a large number of remote satellitelocations as recited in claim 10, wherein said hub site updates saidallocation table every inbound frame.
 13. A method for communicatingwith a large number of remote satellite locations as recited in claim10, wherein said allocation table comprises information relating to anumber of frequencies a remote terminal device is capable of utilizing,a number of mini-slots said remote terminal device may receive, a totalnumber and identification of free inbound ones of said channels andmini-slots, a minimum and assigned maximum load value allocated to eachof said first and second remote terminal device, current inboundresources allocated to each of said plurality of first and second remoteterminal devices, whether said remote terminal device may become anactive site, and whether said remote terminal device has any weightingfactors associated with its load calculations.
 14. A method forcommunicating with a large number of remote satellite locations asrecited in claim 10, wherein said allocation table comprises a list ofall remote sites from which a packet was received during a last measureincrement.
 15. A method for communicating with a large number of remotesatellite locations as recited in claim 14, wherein said measureincrement is one of a multi-slot time period and window.
 16. A methodfor communicating with a large number of remote satellite locations,comprising the steps of: simultaneously communicating in random accessmode with a plurality of a first set of remote terminal devices andcommunicating with a plurality of second remote terminal devices in adedicated mode using the same overlapping channels; preventingcollisions between inbound packets from different ones of said first andsecond remote terminal devices by allocating one of frequency, timeslot, and frequency and time slot to said ones of said first and secondremote terminal devices that generate the most inbound traffic;allocating a mini-slot to each of said first and second remote terminaldevices when there are more active ones of said first and second remoteterminal devices than there are channels; and wherein said first andsecond remote terminal devices have a multi-slot counter, saidmulti-slot counter in each of said first and second remote terminaldevices synchronizing with said hub site and each of said first andsecond remote terminal devices.
 17. A method for communicating with alarge number of remote satellite locations, comprising the steps of:simultaneously communicating in random access mode with a plurality of afirst set of remote terminal devices and communicating with a pluralityof second remote terminal devices in a dedicated mode using the sameoverlapping channels; determining threshold criteria at a hub site todetermine when said first and second set of remote terminal devices areactive; and allocating said channels; calculating load at said hub sitefor each of said first and second remote terminal devices and retainingloads in memory, and wherein said load for each of said first and secondremote terminal devices (L_(new)) is calculated according to thefollowing formula: L_(new) = (L_(old)(1 − τ))^(n) + τ where τ is aconfigurable constant, n is the number of time slots since the last timeslot on which a packet was received from a remote terminal device, andL_(old) is the previous load value of the remote terminal device.
 18. Amethod for communicating with a large number of remote satellitelocations, comprising the steps of: simultaneously communicating inrandom access mode with a plurality of a first set of remote terminaldevices and communicating with a plurality of second remote terminaldevices in a dedicated mode using the same overlapping channels;determining threshold criteria at a hub site to determine when saidfirst and second set of remote terminal devices are active; andallocating said channels; calculating load at said hub site for each ofsaid first and second remote terminal devices and retaining loads inmemory, and wherein said load (L_(new)) for each of said first andsecond remote terminal devices is calculated according to the followingformula: L_(new) = L_(old) * M * (1 − 1/N)^(n) + M/N where M is anormalizing constant M, N is a time constant, which is the number oftime slots in T seconds (where T is a configuration parameter), and τ is1/N, n is the number of time slots since the last time slot on which apacket was received from a remote terminal device, and L_(old) is theprevious load value of the remote terminal device.